The use of metallocene compounds in polymerization catalysts, and the use of metallocene catalysts for polymerization are known. However, there remains an ongoing effort to develop metallocene catalysts, polymerization processes using such catalysts, and polyolefin resins and products made therewith, each having advantageous properties and performance.
There are numerous references discussing metallocene catalyst systems comprising at least two catalyst components, wherein at least one component is a metallocene catalyst. See, for example, U.S. Pat. Nos. 4,530,914, 4,937,299, 5,470,811, 5,516,848, 5,696,045, 6,492,472, 7,141,632, 7,163,906, 7,172,987, and EP-A2-0 743 327, EP-B 1-0 310 734, EP-B 1-516 018.
Additionally, there are also references directed to polymerization processes in which two or more polymerization reactors are joined in series, where one catalyst is used in a first reactor to produce a first polymer that is then fed into a second reactor with the same or different catalyst, typically under different reactor conditions. See, for example, U.S. Pat. No. 5,665,818 and EP-B 1-0 527 221. However, series or multistage reactor processes are expensive and more difficult to operate.
Thus, there remains a need for new processes and catalyst compositions to produce multimodal polyolefin products.